There has been known, for example, a fuel injector of an electromagnetic solenoid type that supplies fuel to cylinders of an internal combustion engine mounted in a vehicle or the like. With regard to the fuel injector of this type, the timing to inject fuel and the amount of fuel to be injected are controlled in such a manner that a valve body (a needle) is driven in a valve-opening direction by controlling a timing and a time period to electrify a coil incorporated in the fuel injector.
In addition, there has been proposed a method of driving the fuel injector, the method involving applying a high voltage to the coil at the beginning of valve opening and, thereafter, applying a low voltage to the coil (i.e., changing the applied voltage from the high voltage to a low voltage). According to this technique, the fuel injector is driven with low power by enhancing the valve-opening responsiveness with the high applied voltage and then changing to the low applied voltage. Further, the high applied voltage is changed to the low applied voltage based on a detection current to be detected by a current detection circuit. Specifically, the applied voltage is changed when it is determined that the detection current reaches a predetermined target peak value.
It is considered that variations in fuel injection devices cause variations in actual drive current. The variations in drive current might cause variations in amount of fuel to be injected. Hence, Patent Literature 1 discloses a technique of correcting a target drive current based on the amount of variations in actual drive current due to the individual difference of the fuel injection devices. The amount of the individual difference of the fuel injection device is stored in a storage part in advance.
However, it is considered that the individual differences in fuel injection devices are not uniform and change with a lapse of time. Therefore, it is considered that technical improvements are necessary for eliminating the variations in amount of fuel to be injected.
With regard to the driving of the fuel injector, there has also been known a technique of feeding a pre-charge current smaller than a current for operating the valve body, to the coil at the beginning of the start to electrify the fuel injector and, subsequently, feeding a drive current for operating the valve body, to the coil. The inventors of this application have focused attention particularly on the condition of energization in a pre-charge period and have made attempts to suppress the variations in fuel to be injected, through improvements in pre-charge control.